1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device using a liquid crystal layer which exhibits a blue phase.
2. Description of the Related Art
In recent years, polymer stabilized blue-phase liquid crystal has been known, which enables high contrast and high-speed response. The polymer stabilized blue-phase liquid crystal exhibits optical isotropy when no voltage is applied thereto and exhibits a characteristic that the optical anisotropy thereof changes when an electric field is applied thereto. A liquid crystal display device described in International Patent Application WO2005/090520 is an example of a liquid crystal display device using the polymer stabilized blue-phase liquid crystal. According to the technology described in International Patent Application WO2005/090520, polymer stabilized blue-phase liquid crystal is sandwiched between a pair of transparent substrates. A pair of comb-like electrodes is formed on one of the transparent substrates. Gray scale signals (video signals, drain signals) corresponding to a display image are supplied to one of the pair of comb-like electrodes (pixel electrode) , while a common signal which is a reference to the gray scale signals is supplied to the other (common electrode), and a liquid crystal display device of an in-plane switching (IPS) system in which an electric field in parallel with surfaces of the transparent substrates is applied is formed.
In such a liquid crystal display device using polymer stabilized blue-phase liquid crystal, in order to reduce the drive voltage, polymer stabilized blue-phase liquid crystal having a high permittivity anisotropy (Δε) is used. However, a liquid crystal layer having a high permittivity anisotropy is thought to be more liable to take in impurity ions, which is thought to be a cause of unsharp moving images and burn-in. A liquid crystal display device described in Japanese Patent Application Laid-open No. 2006-343697 is a liquid crystal display device which is capable of alleviating such an impurity ion imbalance. In the liquid crystal display device described in Japanese Patent Application Laid-open No. 2006-343697, when an image is to be displayed, the pixel electrode and the common electrode are caused to be at a same electric potential.